This invention relates to a power transmission chain belt and, in particular, to a power transmission chain belt for use with a continuously variable transmission (CVT). The belt is comprised of a large number of interleaved link plates which are placed parallel to the chain width direction and carry a number of load blocks or struts for transmission of power to the variable width pulleys of the CVT. The belt is formed of two adjacent chains or chain portions that are offset or phased by one half pitch.
An example of a power transmission chain belt for a CVT is shown in FIG. 12 of the drawings. As shown in FIG. 12, the CVT includes input shaft 101 and output shaft 102, which carry primary (drive) and secondary (driven) pulleys 103, 104, respectively. The chain belt 105 interconnects the primary and secondary pulleys of the CVT.
Primary pulley 103 includes fixed pulley portion 103a, which is fixed to input shaft 101, and moveable pulley 103b, which is moveable along input shaft 101, but does not rotate relative to the shaft. Similarly, secondary pulley 104 includes fixed pulley 104a, which is fixed to output shaft 102, and moveable pulley 104b, which is moveable along output shaft 102, but does not rotate relative to the shaft. The effective diameters of pulleys 103 and 104 are changed by movement of the moveable pulley portions 103b, 104b, which is caused by operation of hydraulic actuators, as is known in the art. In this manner, the speed change ratio between the input and output shafts can be varied continuously.
The chain belt is shown in FIG. 13 and includes two chains or chain portions 110, 111. The chain also includes load blocks or struts 112, which are arranged in the direction of the length of the chain and extend across the width of the chain. The chains 110, 111 are connected alternately by the struts passing between both chain widths. The pulleys contact the outside edges of the struts to pass power between the chain and the pulleys.
The chains are each comprised of link plates that are connected by connecting pins 106, 107. Protrusion 118 is formed at the connection of the chain to each strut to prevent displacement of the strut in the chain width direction (the left to right direction in FIG. 13). Protrusion 118 is formed by a punching tool that is applied to the side of strut 112. Also, the protrusion 118 is formed, as shown in FIG. 14, so that to engage part d or part e of the link at the tips of V-shaped leg parts 121 and 122 or link plate 120. Thus protrusion 118 engages with parts d and e and prevents the release of strut 112 from the chain link plate.
The speed ratio between the input and output shafts is changed by moving the moving pulleys 103b, 104b on the primary and secondary shafts during the operation of the CVT. An offset occurs between pulleys 103 and 104, as shown in FIG. 12, when the speed ratio between the primary and secondary shafts is not one to one. Accordingly, in such a condition, a force acts on the chain belt 105 in the chain width direction, and each strut 112 tends to move in that direction, i.e., the length direction of the strut.
Although release of the strut from the link plate is prevented by protrusion 118 at strut 112, the protrusion is not very large in length. Therefore, the protrusion wears gradually under repeated action of the force in the chain width direction and the release of the strut 112 from link plate 120 may eventually occur.
As shown in FIG. 14, protrusions 118 are placed against part d and part e of the tips of the link plate leg parts 121, 122. The rigidity of the link plate leg parts is not exceptionally high. Therefore, under repeated action of force in the chain width direction, leg parts 121, 122 twist in their thickness direction and, as a result, displacement of the strut 112 gradually increases. Eventually, the protrusion may slide over leg parts 121, 122 so that the strut is no longer held to the link plate.
The present invention is directed to such a situation and offers a chain belt in which the strut is held to the link plate with greater assurance.